I totally agree that aligning with customer need is more than worth the time taken, but that shouldn't be taking 50% of developers time. More like 20% in my opinion. Internal collaboration between devs can take another large chunk of time, but that depends on how experienced (and how good) the developers are.

I've worked on teams with all senior developers where the dev collaboration was mostly covered within that 20%, and minimal synchronisation was needed because we were all on the same page. I've also worked on teams with lots of junior developers, and that did require a lot more detailed planning and discussion that probably did take us close to 50% discussions overall. It was probably a necessary evil, but I wouldn't call it efficient, and it certainly isn't necessary in all cases.